Grid electrode structure and manufacturing method therefor



1955 H. K. GLASER ETAL 3,212,169

GRID ELECTRODE STRUCTURE AND MANUFACTURING METHOD THEREFOR Filed Feb. 9,1962 Fig.|.

WITNESSESI ldlNxEgiToRs d CFO OSEI Ofl ,7 E cYhorles F. Emery. CZMZA [gATTOR United States Patent 3,212,169 GRID ELECTRODE STRUCTURE AND MANU-FACTURING METHOD THEREFOR Harold K. Glaser and Charles F. Emery,Horseheads, N.Y., assignors to Westinghouse Electric Corporation,

East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 9, 1962,Ser. No. 172,192 Claims. (Cl. 29-1555) This invention relates toelectronic discharge devices and more particularly to electrodes forsuch devices and methods of manufacturing thereof.

The characteristics of electronic discharge devices determine the scopeof its use and the elliciency of its operation. The requirements of anelectronic discharge device at very high frequencies impose conditionswhich can only be satisfied by extremely precise constructional featuresto produce the essential electrical constants whereby the highestefliciency is attained. The most important characteristic of an electrondischarge tube is normally in transconductance. The transconductancedepends on the spacing between the cathode, control grid and thediameter of the grid lateral wire and the spacing between the adjacentlateral wires. In order to attain a high transconductance, it isnecessary to reduce the diameter of the control grid lateral wire to apoint where the wire is not self-supporting when wound in a conventionalgrid form. Therefore, the fragile lateral wire must be wound on asupport frame which maintains the spacing between the grid and cathodesubstantially constant within its operational range. In addition, ofcourse, the grid laterals should be of uniform diameter and uniformspacing.

To overcome the problem of support of this fragile wire, it is necessaryto resort to a rigid frame on which the thin helix wire can be wound andfixed thereto. This type of grid structure is referred to in the art asthe frame or planar type grid construction.

The economical mass production of frame grids is a serious problem.Previous solutions have utilized a frame of molybdenum coated with gold.Lateral wires of unplated tungsten are wound onto the coated frame orframes. The wound assembly is then heated in a suitable atmosphere tomelt the gold which in turn solders the lateral tungsten wires to themolybdenum frame. The individual grids are then gold plated to providethe proper finish on the lateral wires to prevent secondary emissionproblems. Gold plated tungsten wires cannot be used in this processbecause good adherence between the gold and tungsten is hard to achieveand the gold tends to form beads at the soldering temperature. Anotherproblem that exists with some lower temperature solders is that it tendsto flow out over the laterals and thereby change its dimensions and thesecondary emission properties of the lateral wire.

It is accordingly an object of the present invention to provide animproved electron discharge device.

It is another object to provide an improved grid electrode structure.

It is another object to provide an improved method of manufacturing agrid electrode structure to provide uniform diameter lateral members.

It is another object to provide an improved method of manufacturing anelectrode that is easy to control and will tolerate a wide latitude ofvariation.

Stated briefly, the present invention provides a rigid frame or planargrid structure for an electron discharge device and the method ofmanufacturing so as to provide uniform spacing and diameter of thelateral grid members. These features are realized in the method ofmanufacturing by providing a brazing material in which a coating3,212,169 Patented Oct. 19, 1965 of copper is applied to the framemember and a coating of gold is applied over the copper coating. Thelateral wires with a gold coating thereon are wound over the frame. Inthe brazing of the lateral members to the frame member, the gold coatingon the lateral wire does not flow and as a result a uniform diameter ofwire is obtained in the final product.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of the novelty whichcharacterize the invention will be pointed out in particularly in theclaims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to theaccompanying drawings, in which:

FIGURE 1 is an electron discharge device partially broken away andincorporating a grid electrode made in accordance with the teachings ofthe invention;

FIG. 2 is a perspective view of the grid electrode incorporated in FIG.1;

FIG. 3 is a perspective view of a grid winding jig used for winding thegrid lateral wire onto a frame grid support member; and,

FIG. 4 is a cross section of the grid structure taken along line IV-IVof FIG. 2 prior to the brazing operation.

Referring in detail to FIG. 1, there is shown an electron dischargedevice embodying the present invention. The device is comprised of anenvelope 10 of suitable material such as glass with an electrodeassembly or cage indicated generally by the character 12 enclosedtherein. The envelope 10 shown is of conventional design and includes atipped off exhaust tube 14 on top of the envelope 10 and a button stemheader 16 closing off the bottom portion of the envelope 10. A pluralityof lead-in members 18 are provided through the button stem 16 forprovoding the necessary voltages to the electrodes therein. Theelectrode assembly within the envelope 10 consists of a cathode 20illustrated as an indirectly heated type cathode. Positioned adjacent tothe cathode 20 is a control grid 22 which is described in more detaillater within the specification. Positioned on the opposite side of thecontrol grid 22 with respect to the cathode 20 is an anode member 21 forcollecting the electrons from the cathode 2t The unit or mount includesa pair of spacer insulating discs 19 of a suitable material such as micawhich supports the electrodes in a fixed position within the electrodecage 12.

The control electrode 22 comprises a frame or disc member 24 of asuitable material such as molydenum with a plurality of lateral wires 30of tungsten wire 31 with a gold coating 32 thereon. The frame or discmember 24 is normally formed by punching sheet metal into the formillustrated in FIG. 2 with an aperture 36 provided in the central regionthereof and which is the active area of the control grid 22.

The molybdenum frame 24 is then plated with copper so as to deposit acoating 26 of copper over the molyb denum frame of a thickness of about.00003 to .00005 inch. A coating 28 of gold is then deposited onto thecopper plated frame by electroplating, for example. The gold coating isa thickness of about .00009 to .00011 inch.

Two frames 24 are then secured as indicated in FIG. 3 and a tungstenwire having a gold coating of about 4% by weight is wound about theframe members. A suitable method of winding the lateral wires 30 ontothe frame members 24 is illustrated in FIG. 3 and simply consists of ajig member 40 to which two disc members 24 are secured by the clampingmembers 42 and 44. The frame members 24 are then rotated and the lateralwire 30 fed thereto to wind the lateral wires 30 about the two framemembers 24. The cut ends of the lateral wire 30 are secured to the frame24 by use of a volatile bonding agent such as Lucite and then the unitis inserted into a brazing furnace. FIG. 4 illustrates the structure ofthe grid 22 prior to insertion in the furnace. The unit is heated in thepresence of Ammogas (a Westinghouse Electric Corporation trademark, nowassigned to the Sunbeam Corporation, for a non-oxidizing atmosphere ofdisassociate-d ammonia, i.e. 3H +N or a hydrogen atmosphere for twominutes at 930 C. This heat treatment produces a gold-copper solidsolution which is rich enough in gold to minimize dissolving the goldcoating 32 from the lateral wire 30. The proper thickness of coatings 26and 28 as specified above also permits the brazing operation to becarried out at a temperature which is low enough to precluderecrystallization of the molybdenum frame. The molybdenum frame,therefore, retains its ductility.

Because of the negature of the gold-copper solid solution, the bond willnot remelt unless it is heated above the original bonding temperature.Another advantage of the structure shown above is that the grid, byproviding the plating on the lateral ends of the frame 24, is alsocapable of suppressing secondary emission.

While there has been shown and described what is at present consideredto be the preferred embodiment of the invention, modifications theretowill readily occur to those skilled in the art. It is not desiredtherefore, that the invention be limited to the specific arrangementsshown and described and it is intended to cover in the appended claimsall such modifications as fall within the true spirit and scope of theinvention.

We claim as our invention:

1. The method of manufacturing a grid electrode which comprises windinga series of turns of a fine wire of gold plated tungsten onto a framesupport member of molybdenum, said support member having a coating ofcopper on said support member and a gold coating on said copper coating,placing said support member and said turns of wire in a non-oxidizingatmosphere, subjecting said turns of Wire and said support member to atemperature sufiicient to produce a gold-copper solid solution on saidsupport member, and cooling said support member and said turns of wirewhereby said turns of wire are secured to said support member.

2. The method of manufacturing a grid electrode which comprisesproviding a molybdenum support member having a coating of copper on saidsupport member and said copper coating having a coating of gold thereon,placing a plurality of tungsten lateral wires having thereon a coatingof gold on said support member, placing said support member and saidlateral wires in a non-oxidizing atmosphere, subjecting said lateralwires and said support member to a temperature suflicient to produce agold-copper solid solution on said support member, and cooling saidlateral wires and said support member whereby said coatings of gold andcopper secure said lateral wires to said support member.

3. The method of manufacturing an electrode including a tungsten wirecoated with gold and a frame member of molybdenum, said methodcomprising the steps of disposing a first layer of copper upon saidframe member, disposing a second layer of gold upon said first layer,placing said wire onto said frame member, subjecting said wire and saidframe member to a temperature sufiicient to produce a gold-copper solidsolution on said frame member, and cooling said frame member and saidwire to thereby secure said wire to said frame member.

4. The method of manufacturing as claimed in claim 3, wherein said stepsof disposing said first and second layers is performed byelectroplating.

5. The method of manufacturing as claimed in claim 3, wherein said firstlayer is disposed upon said frame member to a thickness in the range of.00003 to .00005 inch, and said second layer is disposed on said firstlayer to a thickness in the range of .00009 to .00011 inch.

References Cited by the Examiner UNITED STATES PATENTS 2,678,486 5/54Chick et al 313-348 X 2,897,395 7/59 Miller 29-25.14 X 2,961,759 11/60Weissfloch 29-2514 X 3,069,585 12/62 Katz 2925.14 X

WHITMORE A. WILTZ, Primary Examiner.

LEON PEAR, Examiner.

1. THE METHOD OF MANUFACTURING A GRID ELECTRODE WHICH COMPRISES WINDINGA SERIES OF TURNS OF A FINE WIRE OF GOLD PLATED TUNGSTEN ONTO A FRAMESUPPORT MEMBER OF MOLYBDENUM, SAID SUPPORT MEMBER HAVING A COATING OFCOPPER ON SAID SUPPORT MEMBER AND A GOLD COATING ON SAID COPPER COATING,PLACING SAID SUPPORT MEMBER AND SAID TURNS OF WIRE IN A NON-OXIDIZINGATMOSPHERE, SUB-